1. Field of the Invention
This invention relates to an automatic printing apparatus, and more particularly to an automatic printing apparatus capable of automatically conducting an integrated printing process in continuous manner from the step of forming an image pattern adapted to be repeatedly subjected to an image reproducing process on an image forming element (which is herein defined as an element adapted to receive such image pattern) to obtain a printing master (which is herein defined as an image forming element holding thereon such image pattern), to the printing step.
2. Description of the Prior Art
The present so-called information age is characterized by the multiplicity of the means of information communication, among which the document duplication as a means for transmission of business information not only shows an ever-increasing tendency in the quantity and total expenditure of copying but also is constantly exposed to strong demands from the users for higher copying speed and copying quality, and there has therefore been desired the development of an apparatus for reproducing the image of an original document with a higher speed, a rapid access, a high reliability and an easy maintenance.
Attempting to satisfy such demands there have been proposed various apparatus in the copying and printing fields. Among such apparatus there is already known a printing apparatus provided with an image reproducing station capable of conducting an image reproducing process such as an electrostatic printing process in order to reproduce an original document on a paper sheet or the like.
Such known printing apparatus is ordinarily provided with a master preparing station and plural processing stations certain unit steps such as electrostatic charging, image development, image transfer and image fixing required in the image reproducing process.
In such printing apparatus there is employed a printing master consisting for example of an electroconductive substrate holding thereon an image pattern of an insulating material such as a synthetic resin corresponding to the image of original document to be reproduced, or of a metallic substrate holding thereon such image pattern composed of a photoresist or a photopolymer, or a zinc oxide copying sheet holding thereon an image pattern of an insulating resin formed by a known electrographic process, said image pattern being adapted to be repeatedly subjected to an image reproducing process.
Such masters, however, require preparation processes of multiple steps which are generally complex and time-taking due for example to the use of wet treatment, and a printing apparatus comprising a station for conducting the preparation of such printing master is disadvantageous in lacking rapid access, rapid start, and operational easiness.
Also a printing apparatus utilizing a zinc oxide copying sheet for the printing master requires an elevated number of steps since the preparation of master necessitates the steps of charging, exposure, development and fixing, and also requires an increased dimension of the entire apparatus since the above-mentioned steps of master preparation cannot often be conducted in the processing station for conducting the steps of charging, development, transfer and fixing for electrostatic printing process but have to be conducted in a separate processing station for master preparation.
Furthermore the printing master composed of a zinc oxide copying sheet has a tendency to generate a background fog in the reproduced image due to the inevitable fog potential, and, in order to avoid this phenomenon, it becomes necessary to apply a flash exposure to the master prior to the development step in the electrostatic printing process or to employ a bias potential higher than the normal value at said development step. Also the presence of eventual unevenness in the electric resistance in the zinc oxide photosensitive layer or in the paper substrate results frequently in a corresponding unevenness in the optical density of reproduced image, particularly marked in the medium image density areas, and an additional measure has to be incorporated in order to prevent this phenomenon. The printing master as mentioned above is therefore disadvantageous in that the printing apparatus has to be provided with an additional processing station for conducting such additional measures under precise control.
Furthermore the above-mentioned printing master, wherein the image pattern is composed of a relief structure, has a limitation in the length of run since said relief structure, upon subjected to repeated electrostatic printing process, is damaged by mechanical friction to cause defects in the image pattern or uneven electrostatic charging, thus giving rise to deteriorated quality of reproduced image in proportion to the number of repetition of electrostatic printing process.
Furthermore, the printing apparatus as thus far explained requires a highly trained operator since considerable technical expertise is indispensable in the adjustment and operation of the processing station for the master preparation.
As explained in the foregoing, the known printing apparatus, being associated with the drawbacks in the adjustment and operation of the master preparation process and the processing station therefor and those of the printing master prepared by said process, have much to be improved in order to satisfy the demands of users.